1. Field of the Invention
This invention relates to an operation control mechanism for a camera which performs a sequential control over the camera with an electromagnetic driving member operated by an electromagnetic force.
2. Description of the Prior Art During recent years, there have been proposed various electromagnetically operated shutters of the type having shutter blades opened and closed with an electromagnetic driving member such as a rotor or the like that is operated by an electromagnetic force generated with a current supplied to a coil disposed within a magnetic field. The above-stated electromagnetic driving member dispenses with a charging mechanism and thus permits reduction in size of a shutter mechanism. Meanwhile, recent cameras incorporate varied kinds of automatic operating mechanisms including an automatic focusing mechanism which automatically adjusts the focal point of a photo-taking lens, etc. Hence, it has become necessary to precisely perform a sequential control over these mechanisms. Therefore, as disclosed by U.S. patent application Ser. No. 279,223, now abandoned, there have been proposed some cameras that are arranged, for example, such that automatic focusing action and shutter blade opening-and-closing action are controlled one after the other according to the moving position of a control member. The moving position of the above-stated control member is detected by engaging the control member with an armature which is arranged to have its position shifted by the attraction of an electromagnet and the release therefrom. In cameras of this kind having an electromagnetic driving member and an electromagnetic operated shutter, if the electromagnetically driving member is arranged to be usable in place of the electromagnet, the electromagnetic driving member not only performs its function but also obviates the necessity of the above-stated electromagnet. This would permit reduction in size and cost.
Generally, however, the driving force of the electromagnetic driving member is weak. Therefore, if the moving position of the control member is arranged to be determined by engaging it with the electromagnetic driving member as mentioned above, disengagement between them becomes impossible. In order to solve this problem, the electromagnetic driving member must be arranged to generate a sufficiently large electromagnetic force for the disengagement. Accordingly, to attain the above-stated purpose, it becomes necessary to increase the size of a coil attached to the electromagnetic driving member and the amount of power supply thereto. Further, the increase in size of the coil necessitates an increase in the number of magnets to be used. In other words, use of a larger coil is disadvantageous not only in terms of cost but also in terms of space available within a camera which must be arranged to meet the requirement for reduction in size. Besides, such an arrangement results in an increase in power consumption and thus presents a serious problem for cameras which cannot afford use of batteries of a large capacity again because of the requirement for reduction in size.